Pre‐Referral Provisional Diagnoses and Final Diagnostic Subtypes of Pemphigus at a Regional Tertiary Dermatology Center in Japan: A Single‐Center Retrospective Study

Pemphigus comprises autoimmune blistering diseases with heterogeneous clinical presentations, but pre-referral provisional diagnoses in regional tertiary dermatology practice have been less well characterized. We retrospectively reviewed 35 consecutive patients diagnosed with pemphigus at Toyama University Hospital, a regional tertiary dermatology center in Japan, between January 2011 and May 2026. Final diagnoses were established using clinical, histopathological, immunopathological, and serological findings. We extracted referral characteristics, pre-referral provisional diagnoses, final diagnoses, disease severity, and dates of symptom onset and referral visit from medical records. The median age was 69 years, and 20 patients (57.1%) were female. Final diagnoses were pemphigus vulgaris in 15 patients (42.9%), pemphigus foliaceus in 10 (28.6%), paraneoplastic pemphigus in 3 (8.6%), intercellular IgG/IgA dermatosis in 3 (8.6%), pemphigus herpetiformis in 2 (5.7%), pemphigus vegetans in 1 (2.9%), and unclassified pemphigus in 1 (2.9%). Only 10 patients (28.6%) had pemphigus recorded as the pre-referral diagnosis; other pre-referral diagnoses included impetigo, Behçet's disease, refractory stomatitis, dermatitis/eczema, pemphigoid, and drug eruption. Exploratory cosinor analysis suggested possible annual variation in the interval from symptom onset to referral visit, with longer intervals around winter and shorter intervals around summer. By mapping pre-referral diagnoses to final pemphigus diagnoses, this study highlights heterogeneity in diagnostic subtypes and referral pathways through which pemphigus reaches regional tertiary dermatology care.